1. Field of the Invention
The present invention relates to vacuum exhaust (or evacuation) apparatuses, and vacuum exhaust methods using the vacuum exhaust apparatuses. More particularly, the invention relates to vacuum exhaust apparatuses and vacuum exhaust methods suitably applicable to construction of a vacuum equipment used for deposited film formation, etching, etc. and to mass production of repeating deposited film formation or etching over long periods of time using volumes of gas.
2. Related Background Art
A variety of methods have been proposed heretofore as methods of forming functional deposited films for making solar cells, light-receiving (or photoreceptive) members for electrophotography, and so on. In general, these methods require a vacuum pump capable of evacuating a chamber, a pipe, etc. to a high vacuum, because a reaction has to take place in a high vacuum, and because mixing of impurities can heavily degrade film characteristics, and so on. As such vacuum pumps, oil-sealed rotary pumps are commonly and widely used for reasons of low price, ease to handle, capability of evacuation from the atmospheric pressure, and so on.
Inside the oil-sealed rotary pumps, a small amount of oil circulates in a cylinder. While lubrication and sealing is maintained by the oil, a rotor is rotated in the cylinder to positive displacement exhaustion.
If the oil-sealed rotary pump is used in an environment with a corrosive gas, e.g., on the occasion of carrying out cleaning to remove films and byproducts that are deposited inside a chamber by etching after deposited film formation therein, these gas and powdery products can degrade the lubricity of oil, change the viscosity, make sludge, cause breakage of oil film in the cylinder, decrease an oil circulation amount, and so on. As a result, they will increase frequencies of occurrence of degradation of evacuation performance, seizure, etc. and largely degrade durability of the oil-sealed rotary pump.
Various countermeasures were taken against these problems; e.g., oil filtration to remove dust particles such as the powdery products, sludge, etc. (hereinafter referred to as contaminants) from the oil, use of an oil feed type pump for supply of new oil to an oil tank and discharge of used oil at every rotation of the pump, execution of frequent oil exchanges, use of corrosion-resistant, special mineral oil, employment of a method of introducing an inert gas into the pump case to dilute the corrosive gas, covering each part of the pump with a corrosion-resistant coating, and so on. The countermeasures on the apparatus side include, for example, a method of attaching a cold trap or a dust filter to a pump-inlet-side path in order to remove the contaminants of the corrosive gas, powdery products, and so on. Further, the oil-sealed rotary pump is replaced by another pump such as a dry pump or the like in certain cases.
With the techniques as described above, it was, however, hard to repeatedly operate the vacuum pump continuously over long periods of time using volumes of gas. There can arise a problem, for example, in mass production of solar cells for electric power made of amorphous silicon.
In the continuous and repetitive production over long periods of time using volumes of gas, powdery products made during the production result in making a large amount of sludge. With use of a corrosive gas, corrosiveness thereof may pose a significant problem. Unless this large amount of sludge or corrosive gas is effectively removed, clogging, corrosion, or the like will decrease the oil circulation amount in the oil-sealed rotary pump and deteriorate the oil, so as to cause breakage of oil film and failure in lubrication in the cylinder, which will result in causing degradation of evacuation performance, or failure such as seizure or the like. Since the oil is exposed to a large amount of an active, corrosive gas, particularly, at a junction between the cylinder and the inlet port, the oil is heavily deteriorated there to degrade the oil properties such as lubricity and others considerably. Further, since the cylinder is in contact with vanes at mechanical angles inside the cylinder, the oil film breakage can occur readily, depending upon change in the oil properties and amount. As described above, the prior art of circulating a small amount of oil in the cylinder inevitably suffers the oil film breakage and insufficient lubrication, which was the principal cause of the mechanical failure of the oil-sealed rotary pump.
In order to construct a production apparatus suitable for low cost processes of mass production and the like, the oil-sealed rotary pump is required to be inexpensive and low in instrument cost, present high reliability with less failure, have a simple structure, and allow easy maintenance.
The normal oil filtration mechanisms fail to remove the large amount of sludge produced, which will pose problems of decrease in the oil circulation amount inside the rotary pump because of clogging or the like, occurrence of the oil film breakage and insufficient lubrication in the cylinder, degradation of evacuation performance, seizure, and so on. Particularly, where a large amount of a corrosive gas is used in etching or the like to result in making a large amount of sludge, a large-capacity mechanism capable of removing the large amount of sludge has to be used in order to operate the pump stably. Likewise, where the cold trap or the dust filter is installed, it has to be one with a large capacity. Since these configurations are inserted into an exhaust system and lower the exhaust conductance, the vacuum pump itself has to have a large capacity in order to suppress it. When the conventional oil filtration, cold trap, dust filter, or the like is added, the instrument cost becomes high because of the increase of capacity. It also requires time and cost for maintenance in order to prevent failure of those added components. This poses problems of degrading maintainability and increasing running cost.
On the other hand, since the dry pumps, oil feed type pumps, etc. are generally expensive, use of these pumps raises problems of increasing the instrument cost and, in turn, increasing the production cost.
As for the methods of providing the corrosion-resistant coating over each part of the pump and diluting the corrosive gas with an inert gas, the effect is not sufficient where the large amount of sludge is made or where the large amount of a corrosive gas is repeatedly used over long periods of time.
It is an object of the present invention to solve the above problems separately or all together. Specifically, an object of the present invention is to provide low-cost vacuum exhaust apparatuses that are able to suppress the degradation of lubricity and occurrence of oil film breakage in the pump and that have high reliability and excellent maintainability, even under such circumstances that a large amount of sludge is made and that a large amount of a corrosive gas is repeatedly used over long periods of time, and also provide vacuum exhaust methods using the vacuum exhaust apparatuses.
The inventor conducted elaborate research in order to achieve the above object and accomplished the present invention as a result.
An aspect of the present invention is a vacuum exhaust apparatus comprising: an oil-sealed rotary pump; and an oil supply section for supplying oil to an inlet path of the oil-sealed rotary pump.
The vacuum exhaust apparatus preferably further comprises at least one vacuum pump at a pre-stage before the oil-sealed rotary pump.
The oil supply section may supply oil extracted from the oil-sealed rotary pump.
The oil supply section preferably comprises an oil filtration section.
Preferably, the oil filtration section filtrates the oil extracted from the oil-sealed rotary pump and the oil thus filtrated is supplied to the oil supply section.
Another aspect of the present invention is a vacuum exhaust method using the foregoing vacuum exhaust apparatus, wherein while oil is supplied to the inlet path of the oil-sealed rotary pump to be supplied into a cylinder of the rotary pump, the oil-sealed rotary pump is operated to effect evacuation.
Still another aspect of the present invention is a vacuum exhaust method using the foregoing vacuum exhaust apparatus, wherein while oil extracted from the oil-sealed rotary pump and filtrated is supplied to the inlet path of the oil-sealed rotary pump to be supplied into a cylinder of the rotary pump, the oil-sealed rotary pump is operated to effect evacuation. Preferably, an interior of a vacuum chamber is evacuated while an etching gas to etch a deposited matter away from the interior of the vacuum chamber is supplied into the vacuum chamber.
Preferably, prior to the supply of the etching gas, a deposited film is formed on a substrate in the vacuum chamber and the substrate is taken out thereof.
The present invention provides the low-cost vacuum exhaust apparatuses with excellent maintainability and high reliability, suitable for mass production, and the vacuum exhaust methods using the vacuum exhaust apparatuses.
In the vacuum exhaust apparatuses of the present invention having the above structures, the oil is supplied to the inlet path of the oil-sealed rotary pump. The oil thus supplied is circulated together with the exhaust gas from the vacuum chamber via the inlet port of the rotary pump to be effectively supplied to the junction between the inlet port and the cylinder. The oil is deteriorated most easily at the junction between the inlet port and the cylinder of the rotary pump, but new oil is effectively supplied to this junction, which achieves the effects of improvement in lubricity and prevention of oil film breakage at the portions of contact at mechanical angles between the cylinder and vanes.
Further, since the oil supplied to the junction between the cylinder and the inlet port is drawn into the cylinder, the oil circulating in a small amount is stably circulated inside the rotary pump. This presents the effect of maintaining the amount of oil in the cylinder even in repeated production using volumes of gas over long periods of time and thus effectively maintaining the lubrication and sealing.
As a result, a solution is given to the problems of the failure of seizure or the like and the degradation of evacuation performance and the like due to the film breakage, deterioration of lubricity of oil, and so on. Namely, the reliability and maintainability of the apparatus is enhanced. It also becomes feasible to carry out deposited film formation or etching stably over long periods of time. It is also possible to decrease the production cost. Since the inexpensive rotary pump is used, the instrument cost can be low.
The features of the present invention will be described below in detail by the specification and drawings.